U.S. patent number 5,751,675 [Application Number 08/662,492] was granted by the patent office on 1998-05-12 for recording and/or reproduction apparatus and method for optical record medium.
This patent grant is currently assigned to Sony Corporation. Invention is credited to Katsuji Igarashi, Keiichi Tsutsui.
United States Patent |
5,751,675 |
Tsutsui , et al. |
May 12, 1998 |
Recording and/or reproduction apparatus and method for optical
record medium
Abstract
The invention provides a recording and/or reproduction apparatus
and a recording and/or reproduction method by which information can
be recorded or reproduced accurately onto or from any of a
plurality of record layers of an optical disk. In the recording
and/or reproduction method, after an optical disk is started, an
optimum focus offset position for a predetermined record layer of
the optical disk is searched for. This searching is performed by
varying an offset value stepwise and searching for an offset value
with which the amplitude of a tracking error signal exhibits a
maximum value. After an optimum focus offset position is searched
out, the value of it is stored. Similar processing is performed
also for any other record layer. When an instruction to reproduce a
predetermined record layer is developed in step, focus jumping to
the record layer is performed. Then, an optimum focus offset value
searched out and stored in advance is read out and added to a focus
error signal.
Inventors: |
Tsutsui; Keiichi (Kanagawa,
JP), Igarashi; Katsuji (Tokyo, JP) |
Assignee: |
Sony Corporation (Tokyo,
JP)
|
Family
ID: |
15485050 |
Appl.
No.: |
08/662,492 |
Filed: |
June 13, 1996 |
Foreign Application Priority Data
|
|
|
|
|
Jun 16, 1995 [JP] |
|
|
7-149899 |
|
Current U.S.
Class: |
369/44.27;
369/44.29; 369/44.34; G9B/7.089; G9B/7.093 |
Current CPC
Class: |
G11B
7/094 (20130101); G11B 7/0945 (20130101); G11B
2007/0013 (20130101); G11B 7/0908 (20130101) |
Current International
Class: |
G11B
7/09 (20060101); G11B 7/00 (20060101); G11B
007/00 () |
Field of
Search: |
;369/44.25,44.27,44.28,44.29,32,54,44.34 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hindi; Nabil
Attorney, Agent or Firm: Frommer Lawrence & Haug LLP
Frommer; William S.
Claims
What is claimed is:
1. A recording/reproducing apparatus for an optical storage medium,
comprising:
optical means for recording/reproducing data, represented by a
signal, on/from said optical storage medium;
generating means for generating a focus offset value by
continuously obtaining amplitude values for a first, a second and a
third consecutive sample point of said signal, and by comparing the
amplitude values to each other until a signal position of the
second sample point is determined to be the focus offset value;
and
focus control means for controlling focus of said optical means as
a function of said focus offset value.
2. The apparatus according to claim 1, wherein said generating
means includes search means for searching for the signal position
of the second sample point determined to be an optimum focus offset
value.
3. The apparatus according to claim 2, wherein said search means
includes detection means for detecting a step between said first,
second, and third sample points, and discrimination means for
discriminating the optimum focus offset value.
4. The apparatus according to claim 3, wherein said signal is a
tracking error signal obtained by said optical means.
5. The apparatus according to claim 3, wherein said signal is an
information radio frequency (RF) signal retrieved from said optical
data storage.
6. The apparatus according to claim 3, wherein said signal is a
jitter signal representing disturbances during data
recording/reproducing operations, said jitter signal obtained from
an information radio frequency (RF) signal retrieved from said
optical data storage.
7. The apparatus according to claim 2, wherein said search means
includes storage means for storing the optimum focus offset
value.
8. The apparatus according to claim 2, wherein said optical storage
medium is a recording medium in a shape of a disk.
9. The apparatus according to claim 8, wherein said optical storage
medium has a plurality of information bearing layers.
10. The apparatus according to claim 9, wherein said search means
searches for the optimum focus offset value for each of said
information bearing layers.
11. The apparatus according to claim 10, wherein said search means
includes storage means for storing the optimum focus offset value
for each of said information bearing layers.
12. A recording/reproducing method for an optical storage medium,
comprising the steps of:
recording/reproducing data, represented by a signal, on/from said
optical storage medium;
generating a focus offset value by continuously obtaining amplitude
values for a first, a second and a third consecutive sample point
of said signal, and comparing the amplitude values to each other
until a signal position of the second sample point is determined to
be the focus offset value; and
controlling focus of said optical means as a function of said focus
offset value.
Description
BACKGROUND OF THE INVENTION
This invention relates to a recording and/or reproduction apparatus
and a recording and/or reproduction method, and more particularly
to a recording and/or reproduction apparatus and a recording and/or
reproduction method wherein-focusing control can be performed
rapidly and with certainty upon an optical disk having two or more
record layers.
An optical disk as represented by a compact disk has only one
information record layer. In recent years, it is demanded to
increase the recording capacity. Such increase in capacity can be
achieved, for example, by decreasing the track pitch or by reducing
the pit size. Also an optical disk of a different type has been
proposed wherein it has a plurality of record layers formed therein
in order to further increase the capacity.
FIG. 21 shows an exemplary construction of an optical disk of the
type just mentioned. Referring to FIG. 21, in the optical disk
shown, a record layer A is formed on a disk base plate 101, and
another record layer B is formed on the record layer A. A
protective film 102 is formed on the record layer B.
The disk base plate 101 is made of a transparent material such as,
for example, polycarbonate. The record layer A is formed from a
translucent film while the record layer B is formed from a total
reflection film of, for example, aluminum or a like metal.
In order to reproduce information from the record layer A, a laser
beam is focused on the record layer A as denoted by reference
character L.sub.1, and reflected light from the record layer A is
detected.
On the other hand, in order to reproduce information recorded on
the record layer B, a laser beam is focused upon the record layer B
through the record layer A formed from a translucent film as
denoted by reference character L.sub.2. Then, reflected light from
the record layer B is received through the record layer A and
detected. In this manner, since the record layer A is formed from a
translucent film, information of the record layer B can be read
through the record layer A.
In order to change, while a laser beam is focused upon the record
layer A (or the record layer B), the record layer as an object of
reproduction to the record layer B (or the record layer A), jump
pulses should be applied to a focusing servo loop to cause the
optical head to jump toward the new record layer and then focusing
servo should be applied so that the focusing error signal may be
minimized on the new record layer.
However, the position at which the focusing error signal exhibits a
minimum value is not necessarily an accurate focus position because
of a dispersion of the optical head or the disk in production or
from some other cause. Therefore, normally an offset signal is
added to the focusing error signal so that an optimum focusing
condition can be obtained.
However, in the related art apparatus, the offset value is fixed
irrespective of from which one of record layers information is
reproduced. Accordingly, the related art apparatus has a subject to
be solved in that it is difficult to reproduce information stably
from a plurality of record layers.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a recording
and/or reproduction apparatus and a recording and/or reproduction
method by which information can be recorded or reproduced
accurately onto or from any of a plurality of record layers of an
optical disk.
In order to attain the object described above, according to an
aspect of the present invention, there is provided a recording
and/or reproduction apparatus for an optical record medium, which
comprises an optical means for recording and/or reproducing
information onto and/or from the record medium, a focusing control
means for controlling a focus condition of the optical means in
response to a focus error signal, a production means for producing
a focus offset signal of the optical means based on a signal
reproduced by the optical means, and an addition means for adding
the focus offset signal to the focus error signal. Preferably, the
production means includes a search means for searching for an
optimum focus offset position based on the signal reproduced by the
optical means.
In the recording and/or reproduction apparatus, the optical means
records and/or reproduces information onto and/or from the record
medium, and the focusing control means controls a focus condition
of the optical means in response to a focus error signal. Then, the
production means produces a focus offset signal of the optical
means based on a signal reproduced by the optical means, and the
addition means adds the focus offset signal to the focus error
signal. In order for the production means to produce a focus offset
signal, the search means thereof searches for an optimum focus
offset position based on the signal reproduced by the optical
means.
With the recording and/or reproduction apparatus, since an optimum
focus offset position of light for recording or reproducing
information onto or from the record medium is searched for and a
focus offset signal of the optical means is added to a focus error
signal in response to a result of the search, to or from whichever
one of a plurality of record layers of the record medium
information is to be recorded or reproduced, an optimum focusing
condition can normally be realized irrespective of a dispersion or
a variation with respect to time of the record medium.
According to another aspect of the present invention, there is
provided a recording and/or reproduction method for an optical
record medium, which comprises the steps of recording and/or
reproducing information onto and/or from the record medium by
optical means, producing a focus error signal, producing a focus
offset signal of the optical means based on a signal reproduced by
the optical means, adding the focus offset signal to the focusing
error signal, and controlling a focusing condition of the optical
means based on the focus error signal to which the focus offset
signal is added. Preferably, the step of producing a focus offset
signal includes the step of searching for an optimum focus offset
position based on the signal reproduced by the optical means.
In the recording and/or reproduction method, information is
recorded onto and/or reproduced from the record medium by the
optical means, and a focus error signal is produced. Then, a focus
offset signal of the optical means is produced based on a signal
reproduced by the optical means, and the focus offset signal is
added to the focusing error signal. Then, a focusing condition of
the optical means is controlled based on the focus error signal to
which the focus offset signal is added. In order to control the
focusing condition of the optical means, an optimum focus offset
position is searched for based on the signal reproduced by the
optical means.
With the recording and/or reproduction method, since an optimum
focus offset position of light for recording or reproducing
information onto or from the record medium is searched for and a
focus offset signal of the optical means is added to a focus error
signal in response to a result of the search, to or from whichever
one of a plurality of record layers of the record medium
information is to be recorded or reproduced, an optimum focusing
condition can normally be realized irrespective of a dispersion or
a variation with respect to time of the record medium.
The above and other objects, features and advantages of the present
invention will become apparent from the following description and
the appended claims, taken in conjunction with the accompanying
drawings in which like parts or elements are denoted by like
reference characters.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing an optical disk reproduction
apparatus in which a recording and/or reproduction apparatus
according to the present invention is incorporated;
FIG. 2 is a graph illustrating a relationship between a focus
offset and a tracking error signal;
FIG. 3 is flow chart illustrating operation of the optical disk
reproduction apparatus of FIG. 1;
FIG. 4 is a waveform diagram showing a waveform of a tracking error
signal upon initial operation of the optical disk reproduction
apparatus of FIG. 1;
FIG. 5 is a graph illustrating a principle in detecting an optimum
point of a focus offset by a mountain-climbing method;
FIG. 6 is a flow chart illustrating processing of detecting an
optimum point in accordance with the principle illustrated in FIG.
5;
FIG. 7 is a graph illustrating a principle in detecting an optimum
point from a sudden ascending variation point and a sudden
descending variation point;
FIG. 8 is a flow chart illustrating processing of detecting an
optimum point in accordance with the principle illustrated in FIG.
7;
FIG. 9 is a flow chart illustrating alternative operation for
reproduction of an optical disk;
FIG. 10 is a block diagram of another optical disk reproduction
apparatus which executes the processing of FIG. 9 and in which
another recording and/or reproduction apparatus of the present
invention is incorporated;
FIG. 11 is a flow chart illustrating different operation of the
optical disk reproduction apparatus of FIG. 1;
FIG. 12 is a block diagram showing a further optical disk
reproduction apparatus in which a further recording and/or
reproduction apparatus of the present invention is
incorporated;
FIG. 13 is a block diagram showing a still further optical disk
reproduction apparatus in which a still further recording and/or
reproduction apparatus of the present invention is
incorporated;
FIG. 14 is a block diagram showing a yet further optical disk
reproduction apparatus in which the recording and/or reproduction
apparatus of the present invention is incorporated;
FIG. 15 is a graph illustrating a relationship between a focus
offset and jitters;
FIG. 16 is view illustrating a principle of detecting an optimum
point by a mountain-climbing method;
FIG. 17 is a flow chart illustrating processing of detecting an
optimum point in accordance with the principle of FIG. 16;
FIG. 18 is a graph illustrating a principle of detecting an optimum
point from a sudden descending variation point and a sudden
ascending variation point;
FIG. 19 is a flow chart illustrating processing of detecting an
optimum point in accordance with the principle illustrated in FIG.
18;
FIG. 20 is a block diagram showing a yet further optical disk
reproduction apparatus in which a yet further recording and/or
reproduction apparatus of the present invention is incorporated;
and
FIG. 21 is a sectional view showing an exemplary structure of a
two-layer optical disk.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring first to FIG. 1, there is shown a reproduction apparatus
for an optical disk in which a recording and/or reproduction
apparatus of the present invention is incorporated. Referring to
FIG. 1, an optical disk 1 has a plurality of (2 or more) record
(recording/recordable/recorded) layers. Where the optical disk 1
has two layers, it has such a construction as described hereinabove
with reference to FIG. 21.
The optical disk 1 is rotated at a predetermined speed by a spindle
motor 2. An optical head 3 irradiates a laser beam upon the optical
disk 1 and receives reflected light from the optical disk 1.
A PLL (phase locked loop) circuit 5 binary digitizes a RF (radio
frequency) signal reproduced from a signal recorded on the optical
disk 1 by and outputted from the optical head 3 to produce a binary
RF signal and extracts clocks included in the RF signal to produce
a synchronizing clock signal. A CLV (constant linear velocity)
circuit 6 receives the binary RF signal and the synchronizing clock
signal outputted from the PLL circuit 5 and outputs an error signal
representing an error in phase between them. A switch 8 is
controlled by a control circuit 17 to select one of the output of
the CLV circuit 6 and the output of an initial driving circuit 7
and outputs the selected output to the spindle motor 2.
A data decoder 4 receives the binary RF signal and the
synchronizing clock signal outputted from the PLL circuit 5 and
decodes the binary RF signal with reference to the synchronizing
clock signal.
The optical head 3 produces a focusing error signal in accordance
with, for example, a principle of an astigmatism method and further
produces a tracking error signal in accordance with, for example, a
principle of a push-pull method. A focusing servo circuit 9
receives the focusing error signal outputted from the optical head
3 and drives a focusing coil 12 in response to the focusing error
signal to perform focusing control of the optical head 3 in a
direction perpendicular to (toward or away from) the optical disk
1. A tracking servo circuit 10 receives the tracking error signal
outputted from the optical head 3 and drives a tracking coil 13 in
response to the tracking error signal to perform tracking control
of the optical head 3 in a direction perpendicular to the direction
of a track of the optical disk 1.
A signal outputted from the tracking servo circuit 10 is supplied
to a thread servo circuit 15. The thread servo circuit 15 drives a
thread motor 16 in response to the received signal to move the
optical head 3 in a radial direction of the optical disk 1. The
control circuit 17 controls the focusing servo circuit 9, the
tracking servo circuit 10 and the thread servo circuit 15 as well
as the switch 8.
The reproduction apparatus further includes a tracking error signal
maximum amplitude search circuit 31. The tracking error signal
maximum amplitude search circuit 31 includes a level detection
circuit 41 which detects the level of the tracking error signal
outputted from the optical head 3 and outputs a result of the
detection to a control circuit 42. The control circuit 42 detects
an optimum focus position of the optical head 3 from the output of
the level detection circuit 41.
When the focus offset position of the optical head 3 with respect
to a record layer of the optical disk 1 is varied, the tracking
error signal varies in such a manner as seen in FIG. 2. In
particular, when the position of the optical head 3 is adjusted to
an optimum focus offset position (optimum point), the tracking
error signal exhibits a maximum amplitude, but if the position of
the optical head 3 is displaced from the optimum point, then the
amplitude of the tracking error signal decreases. The control
circuit 42 detects an optimum point in accordance with this
principle.
In order to detect an optimum point, the control circuit 42
controls an offset generation circuit 43 to generate an offset
signal of a predetermined value. The offset signal is added to the
focusing error signal outputted from the optical head 3 by an adder
32. The output of the adder 32 is outputted to the focusing servo
circuit 9.
An optimum focus offset position storage circuit 33 is connected to
the control circuit 42 of the tracking error signal maximum
amplitude search circuit 31. Data of optimum focus offset positions
obtained by searching of the tracking error signal maximum
amplitude search circuit 31 are stored in the optimum focus offset
position storage circuit 33.
FIG. 3 illustrates operation of the reproduction apparatus of FIG.
1. Referring to FIG. 3, first in step S1, disk starting processing
is executed. In particular, when the optical disk 1 is loaded in
position into the reproduction apparatus, the control circuit 17
controls the thread servo circuit 15 to drive the thread motor 16
to move the optical head 3 to a predetermined reference position of
the optical disk 1 such as, for example, the position of an
innermost circumferential track. Further, the control circuit 17
changes over the switch 8 to the initial driving circuit 7 side so
that an initial driving signal outputted from the initial driving
circuit 7 is supplied to the spindle motor 2 via the switch 8.
Consequently, the spindle motor 2 is driven to rotate in response
to the initial driving signal.
Further, the control circuit 17 controls the focusing servo circuit
9 to perform a focusing servoing operation. The optical head 3
irradiates a laser beam upon a default record layer (for example,
the record layer A in FIG. 21) of the optical disk 1 and receives
reflected light of the laser beam from the optical disk 1 to
produce a focusing error signal and a tracking error signal. The
focusing error signal is supplied to the focusing servo circuit 9
via the adder 32. The focusing servo circuit 9 drives the focusing
coil 12 in response to the focusing error signal to control the
position of the optical head 3 in the focusing direction.
The PLL circuit 5 receives a RF signal from the optical head 3 when
the optical head 3 reproduces a signal recorded in the record layer
A of the optical disk 1. The PLL circuit 5 binary digitizes the
received RF signal to produce a binary RF signal and produce a
synchronizing clock signal synchronized with a synchronizing signal
included in the RF signal. The CLV circuit 6 compares the
synchronizing clock signal with the binary RF signal in phase and
outputs an error signal representing an error between them. The
control circuit 17 changes over the switch 8 to the CLV circuit 6
side when a predetermined time elapses after the spindle motor 2 is
started or when the speed of rotation of the spindle motor 2
reaches a predetermined speed. Consequently, the error signal
outputted from the CLV circuit 6 is supplied to the spindle motor
2, and CLV servoing is performed with the error signal. As a
result, the optical disk 1 is driven to rotate in a fixed linear
velocity.
Then, the control sequence advances to step S2, in which optimum
focus searching processing is executed. While the optimum focus
searching processing is hereinafter described, the control circuit
42 of the tracking error signal maximum amplitude search circuit 31
controls the offset generation circuit 43 so that a predetermined
offset signal is added to the focusing error signal by the adder
32. When the focusing condition is not appropriate, the amplitude
of the tracking error signal outputted from the optical head 3 is
small, but when the focusing condition is in an optimum condition,
the amplitude of the tracking error exhibits a maximum value.
Therefore, the amplitude of the tracking error signal is detected
by the level detection circuit 41, and it is discriminated by the
control circuit 42 whether or not a tracking error signal of a
maximum amplitude has been obtained. If it is discriminated that a
tracking error signal of a maximum amplitude has been obtained,
then an offset value which is generated by the offset generation
circuit 43 then is detected.
Then, the control sequence advances to step S3, in which the
optimum focus offset value obtained in step S2 is stored into the
optimum focus offset position storage circuit 33.
After an optimum focus offset position in one record layer (for
example, the record layer A in FIG. 21) is detected, the control
sequence advances to step S4, in which it is discriminated whether
or not similar searching has been performed for all of the record
layers of the optical disk 1. If searching has not been performed
for all of the record layers, the control sequence advances to step
S5, in which record layer changing processing is executed. In
particular, the control circuit 17 controls the focusing servo
circuit 9 so that jump pulses are added to the focusing error
signal (or jump pulses are generated in place of the focusing error
signal). As a result, the focusing coil 12 moves the optical head 3
in the focusing direction in response to the jump pulses so that
the laser beam having been focused upon the record layer A till
then is focused now on the record layer B. After the supply of the
jump pulses is stopped, the ordinary focusing servo loop is put
into a closed condition again to apply servoing so that the
focusing error may be minimized thereby to focus the laser beam
generated by the optical head 3 now upon the record layer B.
Thereafter, the control sequence returns to step S2 to perform
optimum focus searching processing for the record layer B. Then, an
optimum focusing offset value obtained by the optimum focus
searching processing is stored into the optimum focus offset
position storage circuit 33 in step S3.
Where N record layers are formed in the optical disk 1, N optimum
focus offset values are stored into the optimum focus offset
position storage circuit 33 in such a manner as described
above.
After optimum focus offset values (positions) of all of the record
layers of the optical disk 1 are stored, the control sequence
advances from step S4 to step S6, in which the focusing position is
changed to the default record layer set in advance. For example,
the control circuit 17 controls the focusing servo circuit 9 to
generate a required number of jump pulses to focus the laser beam
upon the record layer A nearest to the disk base plate 101.
In this instance, in step S7, the control circuit 42 of the
tracking error signal maximum amplitude search circuit 31 reads the
focus offset value for the record layer A stored in the optimum
focus offset position storage circuit 33 and supplies it to the
offset generation circuit 43. The offset generation circuit 43
generates an offset signal corresponding to the offset value. The
offset signal is added to the focusing error signal by the adder 32
and supplied to the focusing servo circuit 9. The focusing coil 12
is driven by the focusing servo circuit 9 with the focusing error
signal to which the optimum offset value is added. Consequently, an
optimum focusing condition is realized in the record layer A.
Then, the control sequence advances to step S8, in which it is
waited that changing of the record layer to be reproduced is
instructed. When changing of the record layer is instructed, the
control sequence advances to step S9, in which the focus position
is changed to the designated record layer. In particular, in this
instance, the control circuit 17 controls the focusing servo
circuit 9 to generate a predetermined number of jump pulses to
change the focus position, for example, from the record layer A to
the record layer B.
Thereafter, in step S10, reading out processing of an optimum
offset value of the designated record layer is executed. In
particular, the control circuit 42 of the tracking error signal
maximum amplitude search circuit 31 reads out the offset value for
the record layer B stored in the optimum focus offset position
storage circuit 33 and outputs it to the offset generation circuit
43. The offset generation circuit 43 generates an offset signal
corresponding to the offset value. The offset signal is added to
the focusing error signal by the adder 32. The focusing servo
circuit 9 drives the focusing coil 12 in response to the output of
the adder 32 so that an optimum focus condition is realized in the
record layer B (a focus condition wherein the amplitude of the
tracking error signal exhibits a maximum value is realized).
Thereafter, the control sequence returns to step S8 so that the
succeeding processing in steps S8 et seq. is executed
repetitively.
Subsequently, optimum focus searching will be described. As
described hereinabove, upon such searching, tracking servoing is
not yet started. Consequently, the optical head 3 periodically
crosses a plurality of tracks of the optical disk 1. In particular,
since the centers of rotation of the optical disk 1 and the spindle
motor 2 are displaced from each other due to eccentricity between
them, the information reproduction point of the optical head 3 (a
light spot of the laser beam) periodically crosses a plurality of
tracks. As a result, the optical head 3 outputs, for example, such
a tracking error signal as shown in FIG. 4. As seen in FIG. 4, the
tracking error signal exhibits a periodical variation.
The level detection circuit 41 of the tracking error signal maximum
amplitude search circuit 31 detects a peak hold value and a bottom
hold value of the tracking error signal and detects a difference
between them as an amplitude of the tracking error signal. The
amplitude detection signal is supplied to the control circuit 42.
The amplitude of the tracking error signal varies in response to
the focus offset value of the optical head 3 as seen in FIG. 2. The
control circuit 42 detects an optimum point of the focus offset
with which a maximum amplitude of the tracking error signal is
obtained by a so-called mountain-climbing method.
In particular, referring to FIG. 5, the offset signal to be
outputted from the offset generation circuit 43 is successively
incremented by a value .alpha. like S.sub.0, S.sub.1, S.sub.2, . .
. . Then, the amplitude values R.sub.i-1, R.sub.i and R.sub.i+1 of
the tracking error signal at each three successive sampling points
S.sub.i-1, S.sub.i and S.sub.i+1 are compared with each other. When
the amplitude value R.sub.i exhibits the highest value among them
(R.sub.i-1 <R.sub.i >R.sub.i+1), the sampling point S.sub.i
is determined as an optimum point. To this end, the control circuit
42 controls the offset generation circuit 43 to output an offset
value which first exhibits a predetermined initial value and
thereafter successively varies by .alpha.. The offset signal is
added to the focusing error signal by the adder 32 and outputted to
the focusing servo circuit 9.
FIG. 6 illustrates exemplary processing by the mountain-climbing
method when the focus offset value is adjusted. Referring to FIG.
6, first in step S21, an initial value S.sub.0 is placed into Sn.
Then, the focus offset position is set to Sn (in this instance,
Sn=S.sub.0), and an amplitude value of the tracking error signal in
this instance is measured. Then, a result of the measurement is set
to Rn (in this instance, Rn=R0).
In particular, the control circuit 42 controls the offset
generation circuit 43 to generate an offset signal S.sub.0. The
focusing servo circuit 9 controls the focusing coil 12 in response
to the focusing error signal to which the offset signal S.sub.0 is
added by the adder 32 to adjust the focus offset of the optical
head 3.
The level detection circuit 41 detects the amplitude of the
tracking error signal outputted from the optical head 3 and outputs
it to the control circuit 42. The control circuit 42 sets the
amplitude value of the tracking error signal detected then to Rn
(in this instance, Rn=R0).
Thereafter, the control sequence advances to step S22, in which a
value obtained by addition of S.sub.0 and .alpha. is placed into
Sn+. In other words, the following equation is calculated:
Then, the control circuit 42 controls the offset generation circuit
43 to generate such offset signal Sn+ (=S.sub.1). In particular,
the control circuit 42 controls the offset generation circuit 43 to
generate an offset value which is higher by .alpha. than the offset
signal Sn generated in step S21. Since the focusing servo circuit 9
controls the focusing coil 12 in response to the focusing error
signal to which the offset value is added, the optical head 3
further varies the focus offset thereof by an amount corresponding
to the offset value .alpha..
The level detection circuit 41 detects the amplitude of the
tracking error signal outputted from the optical head 3 then. The
control circuit 42 sets the amplitude of the tracking error signal
detected by the level detection circuit 41 then to Rn+ (in this
instance, R0+=R.sub.1).
Then, the control sequence advances to step S23, in which a value
lower by .alpha. than S.sub.0 is placed into Sn-. In other words,
the following equation is calculated:
In particular, the control circuit 42 controls the offset
generation circuit 43 to generate a value lower by a than the
offset signal Sn (in this instance, Sn=S.sub.0) generated in step
S2. Since the focusing error signal to which the offset signal Sn-
is added is supplied to the focusing coil 12 via the focusing servo
circuit 9, the focus offset of the optical head 3 is varied by an
amount corresponding to the offset value -.alpha. from that when
the offset value S.sub.0 was generated.
Then, the level detection circuit 41 thereupon detects the
amplitude of the tracking error signal outputted from the optical
head 3 and outputs it to the control circuit 42. The control
circuit 42 places the amplitude value of the tracking error signal
then into Rn- (in this instance, Rn-=R.sub.0 -).
By the processing in steps S21 to 23 described above, the amplitude
value Rn (=R.sub.0) of the tracking error signal when the offset
value to be added to the focusing error signal is set to the
initial value S.sub.0, the amplitude value Rn+ (=R.sub.0 +=R.sub.1)
of the tracking error signal when the offset signal is increased by
.alpha. and the amplitude value Rn- (=R.sub.0 -) when the offset
signal is decreased by .alpha. are obtained as illustrated in FIG.
5.
Thereafter, the control sequence advances to step S24, in which it
is discriminated whether or not Rn is equal to Rn+ or Rn is higher
than Rn+ and equal to Rn- or else Rn is higher than Rn-. In other
words, it is discriminated whether or not Rn is higher than Rn- and
Rn+ (that is, whether or not Rn is the highest value).
Normally, as shown in FIG. 5, the amplitude Rn (=R.sub.0) of the
tracking error signal when the offset signal is S.sub.0 is higher
than the amplitude value Rn- (=R.sub.0 -) when the offset signal is
lower by .alpha., but is lower than the amplitude Rn+ (=R.sub.0
+=R.sub.1) of the tracking error signal when the offset signal is
higher by .alpha.. Therefore, in this instance, the control
sequence advances to step S25, in which it is discriminated whether
or not Rn+ is higher than Rn-. In this instance, since Rn+
(=R.sub.0 +=R.sub.1) is higher than Rn- (=R.sub.0 -) (since the
values are within a section of the curve of FIG. 5 within which the
curve exhibits a rightwardly ascending slope in FIG. 5), the
control sequence advances to step S26.
In step S26, Sn (=S.sub.0) till then is placed into Sn-. Then, Sn+
(=S.sub.1) till then is placed into new Sn, and Rn (=R.sub.0) till
then is placed into Rn-, and then Rn+ (=R.sub.1) till then is
placed into Rn. Then, a value (=S.sub.0 +2.alpha.=S.sub.2) obtained
by adding .alpha. to new Sn (=S.sub.0 +.alpha.=S.sub.1) is placed
into Sn+. In other words, the following equation is calculated:
The control circuit 42 controls the offset generation circuit 43 to
generate Sn+ (=S.sub.2) as an offset signal. In other words, the
control circuit 42 controls the offset generation circuit 43 to
generate an offset Sn+ (=S.sub.0 +2.alpha.=S.sub.2) higher by
.alpha. than Sn+ (=S.sub.0 +.alpha.) generated in step S22. Then,
the amplitude of the tracking error signal detected then is placed
into Rn+ (=R.sub.1 +=R2).
In other words, as a result, the amplitude values of the tracking
error signal at the three sampling points S.sub.0, S.sub.1 and
S.sub.2, which have been shifted rightwardly by .alpha. from those
till then in the condition shown in FIG. 5, are placed in Rn-
(=R.sub.0), Rn (=R.sub.1) and Rn+ (=R2).
Then, the control sequence returns to step S24, in which it is
discriminated whether or not Rn is higher than Rn- and Rn+. When Rn
is not the highest value, the control sequence advances to step
S25, in which it is discriminated again whether or not Rn is higher
than Rn-. When Rn+ is higher than Rn-, the control sequence
advances to step S26, in which similar processing is repeated.
Then, if the section for sampling is shifted in the rightward
direction in FIG. 5 until Sn comes to an optimum point, then the
amplitude value Rn obtained then is higher than Rn- and besides
higher than Rn+. In other words, Rn exhibits the highest value.
Thus, in this instance, the control sequence advances to step S28,
in which the value of Sn then is set as an optimum value with which
the amplitude Rn of the tracking error signal exhibits a maximum
value. In other words, the control circuit 42 thereafter controls
the offset generation circuit 43 to continuously generate the
offset signal Sn as the optimum value.
On the other hand, when sampling is proceeding in a section in
which the curve in FIG. 5 exhibits a rightwardly descending slope,
the value of Rn+ exhibits a value lower than Rn-. Thus, in this
instance, the control sequence advances from step S25 to S27, in
which Sn till then is placed into Rn+, Sn- till then is placed into
Sn, Rn till then is placed into Rn+, and Rn- till then is placed
into Rn. Then, a value lower by .alpha. than new Sn is placed into
Sn-. In other words, the following equation is calculated:
In particular, referring to FIG. 5, the sampling point on the left
side is sampled with Sn-. Then, the amplitude value of the tracking
error signal when the offset signal Sn- is generated by the offset
generation circuit 43 is detected. The thus detected amplitude
value is placed into Rn-.
Then, the control sequence returns to step S24, in which it is
discriminated whether or not Rn is higher than Rn- and Rn+. Since
Rn is still lower than Rn- in the portion of the characteristic of
the rightwardly descending slope in FIG. 5, the control sequence
advances to step S25 and then from step S25 to step S27 to repeat
similar processing. Then, when the sampling point successively
advances in the leftward direction (toward an optimum point) in
FIG. 5 until Sn reaches an optimum point, Rn exhibits a value
higher than Rn+ and higher than Rn-. In this instance, the control
sequence advances from step S24 to step S28, in which the value of
the offset signal then is determined as an optimum value.
Thereafter, the control circuit 42 controls the offset generation
circuit 43 to successively generate the optimum value.
While, in the description above, an optimum point (maximum value)
is detected by the so-called mountain-climbing method, the optimum
point may be determined otherwise in such a manner as illustrated,
for example, in FIG. 7. In particular, in the method illustrated in
FIG. 7, the offset signal is successively varied by .alpha. to
sample the tracking error signal for the entire period from S.sub.0
to Sn first. Then, in this instance, the offset signal which
corresponds to a point of a sudden ascending variation of the
tracking error signal obtained by the sampling is detected as
Sm.sub.1 whereas the offset signal which corresponds to a point of
a sudden descending variation of the tracking error signal is
detected as Sm.sub.2. Then, a middle point between the variation
points Sm.sub.1 and Sm.sub.2 is determined as an optimum point
(adjustment point).
FIG. 8 illustrates an example of processing when an optimum point
is detected based on the method illustrated in FIG. 7. In the
processing illustrated in FIG. 8, first in step S31, a variable n
is initially set to 0, and in step S32, the following equation is
calculated:
where SMIN is the minimum value of the offset adjustment value, and
.alpha. is the width or step size by which the offset signal is
varied stepwise.
In the present case, since n=0, S[0] is placed into SMIN.
The control circuit 42 controls the offset generation circuit 43 to
generate the value S[n] (in the present case, S[0]=SMIN).
Thereafter, the amplitude of the tracking error signal then is
detected by the level detection circuit 41. The value thus detected
is placed into R[n] (=R[0]).
Then, the control sequence advances to step S33, in which the
variable n is incremented by 1 (n is set to n=1). In step S34, it
is discriminated whether or not the variable n after incremented is
lower than NUM. The character NUM represents a value given, where a
maximum value of the offset value is represented by SMAX, by
(SMAX-SMIN)/.alpha.. In other words, NUM represents a sample number
in the offset scanning range.
Where n is lower than NM, since this signifies that sampling is not
yet completed for all sampling points, the control sequence returns
to step S32, in which the following equation is calculated:
In other words, in this instance, a value higher by .alpha. than
SMIN is set as an offset signal S[1]. Then, the amplitude of the
tracking error signal when the offset signal S[1] is generated is
measured, and the thus measured value is set as R[1].
Thereafter, the control sequence advances to step S33, in which the
variable n is incremented by one, in this instance, to n=2. When it
is discriminated in step S34 that the variable n (=2) is lower than
NUM, the control sequence returns to step S32 so that similar
processing is executed repetitively. Amplitude values R.sub.0 to Rn
of the tracking error signal at the sampling points of S.sub.0 to
Sn shown in FIG. 7 are obtained in this manner.
When the sampling in the search range is completed in such a manner
as described above, the variable n becomes equal to NUM.
Consequently, the control sequence now advances from step S34 to
step S35, in which the variable n is initialized to 1. Then, in
step S36, it is discriminated whether or not the difference between
the amplitude value R[n] at the current reference point and the
preceding amplitude value R[n-1] is higher than a reference value
Th set in advance. In the present case, it is discriminated whether
or not the value of R[1]-R[0] is higher than Th. Since the curve in
FIG. 7 exhibits a rightwardly descending characteristic within a
first period of the sampling range as seen in FIG. 7, R[1] is
sufficiently higher than R[0] (the difference (R[1]-R[0]) between
them is higher than Th). Therefore, the control sequence advances
to step S37, in which a middle value between the sampling points
S[n] and S[n-1] is set as a variation point Sm.sub.1. In other
words, the following equation is calculated:
In the present case, a middle point between S[1] and S[0] is set as
Sm.sub.1.
Thereafter, the control sequence advances to step S38, in which the
variable n is incremented by 1 (to n=2), and then to step S39, in
which it is discriminated whether or not the variable n is lower
than NUM. When the variable n is lower than NUM, the control
sequence returns to step S36, in which it is discriminated whether
or not the value of R[2]-R[1] is higher than Th. As seen in FIG. 7,
within a period within which the tracking error signal exhibits a
great variation, the difference between two sample values is higher
than the reference value Th. Thus, the control sequence advances
again to step S37, in which Sm.sub.1 is set to the value of
(S[2]+S[1])/2. In other words, a value at the sample point spaced
rightwardly by .alpha. from the preceding sample point is set as
Sm.sub.1.
Then, in step S38, the variable n is incremented by 1 again to n=3,
whereafter the control sequence returns from step S39 to step S36
to execute similar processing repetitively.
Then, as the sampling point moves rightwardly in FIG. 7, the rate
of change of the tracking error signal degreases gradually. Then,
when it is discriminated that the value of R[n]-R[n-1] is lower
than Th, the control sequence advances from step S36 to step S40.
In other words, in this instance, a point of variation at which the
rate of change of the amplitude of the tracking error signal
changes from a section in which it is high to another section in
which it is low (a sudden ascending variation point) is set as
Sm.sub.1.
In steps S40 et seq., a point of variation at which the rate of
change of the amplitude of the tracking error signal changes from a
section in which it exhibits a gradual decrease to another section
in which it exhibits a sudden decrease is detected as a sudden
descending variation point Sm.sub.2.
To this end, in step S40, it is discriminated whether or not the
value of R[n-1]-R[n] is lower than the reference value Th. As seen
from FIG. 7, within a period within which the sample value R[n-1]
on the left side is lower than the sample value R[n] on the right
side (within a period within which the curve exhibits a rightwardly
ascending slope) as well as within a period within which the sample
value R[n] on the right side is lower than the sample value R[n-1]
on the left side but the difference between them is small, the
value of R[n-1] is lower than the reference value Th. Consequently,
the control sequence advances from step S40 to step S41, in which a
middle value between S[n] and S[n-1] is set as Sm.sub.2. In other
words, the following equation is calculated:
Then, n is incremented by 1 in step S42, and in step S43, it is
discriminated whether or not the variable n is lower than NUM-1
(whether or not the search range has reached the right end in FIG.
7). When the variable n is lower then NUM-1, the control sequence
returns to step S40, in which similar processing is repeated for
two sample values on the right side shifted by one sample distance
in FIG. 7. Then, when the difference between the two sample values
is lower than the reference value Th, the control sequence advances
again to step S41, in which a middle value between the two sampling
points is set as Sm.sub.2.
When the sampling point is successively shifted in the rightward
direction in FIG. 7 in this manner until the sample value R[n] on
the right side in FIG. 7 exhibits a sudden decrease from the sample
value R[n-1] on the left side, the difference between them
(R[n-1]-R[n]) becomes equal to or higher than the reference value
Th. In this instance, a middle value between the sample points
S[n-1] and S[n-2] is placed into Sm.sub.2. Thus, the value then is
determined as a sudden descending variation point Sm.sub.2.
Since the sudden ascending variation point Sm.sub.1 has been
determined in step S37 and the sudden descending variation point
Sm.sub.2 has been determined in step S41 in such a manner as
described above, the control sequence now advances to step S44, in
which a middle point between the variation points Sm.sub.1 and
Sm.sub.2 is determined as an optimum point. In other words, the
value of (Sm.sub.1 +Sm.sub.2)/2 is set as an optimum point.
It is to be noted that, when it is discriminated in step S39 that
the variable n is equal to or higher than NUM, the control sequence
advances from step S39 to step S40. On the other hand, when it is
discriminated in step S43 that the variable n is equal to or higher
than NUM-1, the control sequence advances from step S43 to step
S44.
While, in the operation of the reproduction apparatus illustrated
in FIG. 3, when the optical disk 1 is loaded in position into the
reproduction apparatus, optimum focus offset positions of all
record layers of the optical disk 1 are searched out and stored in
advance, it is otherwise possible to search for an optimum focus
offset position each time the object record layer for focusing is
changed.
FIG. 9 illustrates such processing as just described. Referring to
FIG. 9, first in step S51, the production apparatus waits until an
instruction to change the object record layer upon which light is
to be focused is developed. When a changing instruction is
developed, the control sequence advances to step S52, in which jump
pulses with which the focus position is to be jumped to the
designated record layer are generated by the focusing servo circuit
9. Consequently, the optical head 3 is jumped in the focusing
direction to a position at which it can be focused upon the
designated record layer.
Then, the control sequence advances to step S53, in which
processing of searching for an optimum focus position in the record
layer to which the optical head 3 has just been jumped is executed.
The optimum focus searching processing in this instance is similar
to the processing of step S2 in FIG. 3.
When the optimum focus searching processing comes to an end in step
S53, the control sequence returns to step S51 so that similar
processing is executed repetitively. In other words, such
processing as described above is performed each time the object
record layer is changed.
Accordingly, in this instance, the control circuit 42 of the
tracking error signal maximum amplitude search circuit 31 of the
reproduction apparatus for the optical disk 1 controls, when it
controls the offset generation circuit 43 to generate an offset
signal with which the tracking error signal detected by the level
detection circuit 41 exhibits a maximum amplitude, the offset
generation circuit 43 to thereafter generate the offset signal
continuously. As a result, where the present processing is
employed, the optimum focus offset position storage circuit 33
shown in FIG. 1 is unnecessary.
FIG. 11 illustrates a further example of operation a reproduction
apparatus for an optical disk. While, in the optimum focus
searching processing illustrated in FIG. 9, the processing is
executed each time the object record layer is changed, this
requires much time until it becomes possible, each time the record
layer is changed, to actually reproduce data. The processing
illustrated in FIG. 11 can reduce the time.
Referring to FIG. 11, first in step S61, the production apparatus
waits until an instruction to change the object record layer is
developed. When an instruction to change the object record layer is
developed, the control sequence advances to step S62, in which jump
pulses are generated from the focusing servo circuit 9 to move the
optical head 3 toward the object record layer.
Thereafter, the control sequence advances to step S63, in which
processing of detecting the amplitude of the tracking error signal
then is executed. In particular, the control circuit 42 of the
tracking error signal maximum amplitude search circuit 31 reads an
amplitude value of the tracking error signal outputted from the
level detection circuit 41 then and places the thus read value into
Rn.
Where the present processing is employed, the reproduction
apparatus is constructed in such a manner as shown in FIG. 1. The
detected value Rn is supplied to and stored into the optimum focus
offset position storage circuit 33. In the optimum focus offset
position storage circuit 33, also an amplitude of the tracking
error detected during reproduction of the preceding record layer is
stored as R.sub.p. Thus, in step S64, it is discriminated whether
or not the value of R.sub.p -Rn is higher than a reference value T
set in advance.
In particular, when the amplitude Rn obtained at present is higher
than the amplitude R.sub.p obtained in the preceding operation
cycle or the amplitude Rn is lower than the amplitude R.sub.p but
the difference between them is smaller than the reference value T,
the focus offset value is maintained determining that data can be
reproduced with sufficient stability without particularly changing
the focus offset value. In other words, the same offset value as
that upon reproduction of the preceding record layer is generated
continuously. Then, the control sequence returns to step S61 so
that the processing in steps S61 et seq. is executed
repetitively.
On the other hand, when the amplitude Rn at present is smaller than
the preceding amplitude R.sub.p and the difference between them is
larger than the reference value T, the control sequence advances
from step S64 to step S65, in which optimum focus searching
processing is executed. The optimum focus searching processing is
similar to the processing in step S2 of FIG. 3 or in step S53 of
FIG. 9. Then, when the optimum focus searching processing comes to
an end, the control sequence returns to step S61 so that the
processing in steps S61 et seq. is executed repetitively.
In short, in the present processing, since focus searching
processing is executed only when the amplitude of the tracking
error signal does not exhibit a sufficient magnitude originating
from a displacement of the focus offset, the number of times by
which focus searching processing is executed can be reduced
comparing with that in the processing illustrated in FIG. 9.
Consequently, reproduction of data from the record layer can be
started more rapidly as much.
FIG. 12 shows another embodiment of a further optical disk
reproduction apparatus in which a further recording and/or
reproduction apparatus of the present invention is incorporated. In
the present embodiment, the tracking error signal maximum amplitude
search circuit 31 of FIG. 1 is replaced by a RF signal maximum
amplitude search circuit 51. A RF signal outputted from the optical
head 3 is inputted to the RF signal maximum amplitude search
circuit 51.
The RF signal maximum amplitude search circuit 51 includes a level
detection circuit, a control circuit and an offset generation
circuit (not shown) similarly to the tracking error signal maximum
amplitude search circuit 31 shown in FIG. 1. The other construction
of the reproduction apparatus is similar to that of the
reproduction apparatus shown in FIG. 1.
In particular, in the embodiment of FIG. 12, when an instruction to
start a reproduction operation is developed, the control circuit 17
first feeds the optical head 3 to the position of the innermost
circumferential track of the optical disk 1 and then drives the
spindle motor 2 to rotate the optical disk 1. Thereafter, the
focusing servo circuit 9 and the tracking servo circuit 10 are both
put into an operative condition. Consequently, focusing servoing
and tracking servoing are applied.
The relationship between the focus offset and the amplitude of the
RF signal in this condition is illustrated by graphs in FIGS. 2, 5
and 7. In particular, when the focus offset of the optical head 3
with respect to a record layer of the optical disk 1 is set to an
optimum value, the RF signal exhibits a maximum amplitude.
Accordingly, by detecting a maximum value of the amplitude of the
RF signal by means of the RF signal maximum amplitude search
circuit 51 in a similar manner as in that when a maximum value of
the amplitude of the tracking error signal is detected, an optimum
point can be searched for and set. Since the processing is similar
to that of the optical disk reproduction apparatus described
hereinabove with reference to FIG. 1, description thereof is
omitted here.
On the other hand, when optimum focus searching processing is
executed using a RF signal each time the object record layer is
changed as shown in FIG. 9, the optimum focus offset position
storage circuit 33 shown in FIG. 12 is unnecessary. Consequently,
the reproduction apparatus has such a construction which eliminates
the optimum focus offset position storage circuit 33 as shown in
FIG. 13.
Further, when searching for a maximum amplitude is performed using
a RF signal, where the processing illustrated in FIG. 3 or 11 is
employed, the reproduction apparatus requires the optimum focus
offset position storage circuit 33 as seen in FIG. 12.
FIG. 14 shows a yet further optical disk reproduction apparatus
embodying the present invention. In the present embodiment, a
minimum jitters search circuit 61 is provided in place of the
tracking error signal maximum amplitude search circuit 31 of the
embodiment of FIG. 1. A jitters measurement circuit 62 detects
jitters from an output of the PLL circuit 5 and outputs the
detected jitters to the minimum jitters search circuit 61. The
minimum jitters search circuit 61 includes, similarly to the
tracking error signal maximum amplitude search circuit 31 shown in
FIG. 1, a level detection circuit, a control circuit and an offset
generation circuit not shown.
The other construction of the optical disk reproduction apparatus
of FIG. 14 is similar to that of the optical disk reproduction
apparatus of FIG. 1.
The jitters measurement circuit 62 detects an absolute value of the
phase difference between a binary RF signal and a synchronizing
clock signal outputted from the PLL circuit 5 and outputs it as
jitters to the minimum jitters search circuit 61. The relationship
between the jitters and the focus offset is such as illustrated in
FIG. 15.
In particular, as seen from FIG. 15, when the focus offset of the
optical head 3 with respect to the optical disk 1 is optimum, the
jitters are minimum, and as the focus offset is displaced from the
optimum position, jitters increase. By detecting a minimum value of
the jitters, an optimum point of the focus offset of the optical
head 3 with respect to the optical disk 1 can be determined.
The minimum value of the jitters can be calculated by such a
mountain-climbing method as illustrated in FIG. 16. Referring to
FIG. 16, the sampling point is successively shifted in an
increasing direction by .alpha.. When the central sample value is
lower than the left and right sample values, a sample point at
which the central sample value is obtained is set as an optimum
point.
FIG. 17 illustrates an example of processing of determining a
minimum value of jitters by the mountain-climbing method.
Referring to FIG. 17, first in step S71, an initial value S.sub.0
is placed into Sn. Then, the focus offset position is set to Sn (in
the present instance, Sn=S.sub.0). Further, the amplitude value
(magnitude) of jitters in this instance is measured and a result of
the measurement is placed into Rn (in the present instance,
Rn=R.sub.0).
In particular, the control circuit 42 controls the offset
generation circuit 43 to generate an offset signal S.sub.0. The
focusing servo circuit 9 controls the focusing coil 12 in response
to a focusing error signal to which the offset signal S.sub.0 is
added by the adder 32 to adjust the focus offset position of the
optical head 3.
The level detection circuit 41 thereupon detects the amplitude of
jitters outputted from the jitters measurement circuit 62 and
outputs it to the control circuit 42. The control circuit 42 places
the amplitude value detected then into Rn (in the present instance,
Rn=R.sub.0).
Thereafter, the control sequence advances to step S72, in which a
value obtained by addition of S.sub.0 and .alpha. is placed into
Sn+. In particular, the following equation is calculated:
Then, the control circuit 42 controls the offset generation circuit
43 to generate the offset signal Sn+ (=S.sub.1). In particular, the
control circuit 42 controls the offset generation circuit 43 to
generate an offset value higher by .alpha. than the offset value
generated in step S71. Since the focusing servo circuit 9 controls
the focusing coil 12 in response to the focus error signal to which
the offset value is added, the optical head 3 further varies the
focus offset position of the optical head 3 by an amount
corresponding to the offset value .alpha..
The level detection circuit 41 in this instance detects the
amplitude of jitters outputted from the jitters measurement circuit
62. The control circuit 42 places the amplitude of jitters then
detected by the level detection circuit 41 into Rn+ (in this
instance, R.sub.0 +=R.sub.1).
Subsequently, the control sequence advances to step S73, in which a
value lower by .alpha. than S.sub.0 is placed into Sn-. In other
words, the following equation is calculated:
In particular, the control circuit 42 controls the offset
generation circuit 43 to generate a value lower by .alpha. than the
offset signal Sn (in this instance, Sn=S.sub.0) generated in step
S71. Since the focus error signal to which the offset signal Sn- is
added is supplied to the focusing coil 12 via the focusing servo
circuit 9, the focus offset position of the optical head 3 is
varied by an amount corresponding to the offset value -.alpha. from
that when the offset value S.sub.0 was generated.
The level detection circuit 41 detects the amplitude of jitters
outputted from the jitters measurement circuit 62 then and outputs
it to the control circuit 42. The control circuit 42 places the
amplitude value of jitters then into Rn- (in this instance,
Rn-=R.sub.0 -).
By the processing in steps S71 to S73 described above, the
amplitude value Rn (=R.sub.0) of jitters when the offset value to
be added to the focus error signal is set to the initial value
S.sub.0, the amplitude value Rn+ (=R.sub.0 +=R.sub.1) of jitters
when the offset signal is increased by .alpha. and the amplitude
value Rn- (=R.sub.0 -) of jitters when the offset value is
decreased by .alpha. are obtained as seen in FIG. 16.
Thus, the control sequence advances to step S74, in which it is
discriminated whether or not Rn is equal to or lower than Rn+ and
besides Rn is equal to or lower than Rn-. In other words, it is
discriminated whether or not Rn is lower than Rn- and Rn+ (whether
or not Rn is a minimum value).
Normally, although the amplitude Rn (=R.sub.0) of jitters when the
offset signal is S.sub.0 is lower than the amplitude value Rn-
(=R.sub.0 -) when the offset signal is lower by .alpha. as seen in
FIG. 16, it is higher than the amplitude Rn+ (=R.sub.0 +=R.sub.1)
of jitters when the offset signal is higher by .alpha.. Thus, in
this instance, the control sequence advances to step S75, in which
it is discriminated whether or not Rn+ is lower than Rn-. In this
instance, since Rn+ (=R.sub.0 +=R.sub.1) is lower than Rn-
(=R.sub.0 -) (since the curve portion is in a rightwardly
descending section in FIG. 16), the control sequence advances to
step S76.
In step S76, Sn (=S.sub.0) till then is placed into Sn-. Then, Sn+
(=S.sub.1) till then is placed into new Sn, Rn (=R.sub.0) till then
is placed into Rn-, and Rn+ (=R.sub.1) till then is placed into Rn.
Further, a value (=S.sub.0 +2.alpha.=S2) obtained by addition of
.alpha. to new Sn (=S.sub.0 +.alpha.=S.sub.1) is placed into Sn+.
In other words, the following equation is calculated:
The control circuit 42 controls the offset generation circuit 43 to
generate Sn+ (=S2) as an offset signal. In particular, the control
circuit 42 controls the offset generation circuit 43 to generate an
offset Sn+ (=S.sub.0 +2.alpha.=S2) higher by a than Sn+ (=S.sub.0
+.alpha.) generated in step S72. Then, the amplitude of jitters
detected then is placed into Rn+ (=R.sub.1 +=R2).
In other words, as a result, the amplitude values of jitters at the
three sampling points S.sub.0, S.sub.1 and S.sub.2 shifted
rightwardly by .alpha. from those in the preceding scanning are set
to Rn- (=R.sub.0), Rn (=R.sub.1) and Rn+ (=R.sub.2),
respectively.
Then, the control sequence returns to step S74, in which it is
discriminated whether or not Rn is lower than Rn- and Rn+. When Rn
is not a minimum value, the control sequence advances to step S75,
in which it is discriminated again whether or not Rn+ is lower than
Rn-. When Rn+ is lower than Rn-, the control sequence advances to
step S76 so that similar processing is repeated.
Then, when the section for sampling is successively shifted in the
rightward direction in FIG. 16 until Sn reaches an optimum point,
the amplitude value Rn obtained then is lower than Rn- and lower
than Rn+. In other words, Rn is a minimum value. Thus, in this
instance, the control sequence advances from step S74 to step S78,
in which the value of Sn then is set as an optimum value with which
the value of jitters exhibits a maximum value. In other words, the
control circuit 42 controls the offset generation circuit 43 to
generate the offset signal Sn as an optimum value continuously.
On the other hand, when sampling is proceeding in a rightwardly
ascending section in FIG. 16, the value of Rn+ is higher than Rn-.
Thus, in this instance, the control sequence advances from step S75
to step S77, in which Sn till then is placed into Sn+, Sn- till
then is placed into Sn-, Rn till then is placed into Rn+, and Rn-
till then is placed into Rn. Then, a value lower by .alpha. than
new Sn is placed into Sn-. In other words, the following equation
is calculated:
In particular, the sampling point on the left side in FIG. 16 is
sampled with Sn-. Then, the amplitude of jitters when the offset
signal Sn- is generated from the offset generation circuit 43 is
detected, and the detected amplitude value is placed into Rn-.
Then, the control sequence returns to step S74, in which it is
discriminated whether or not Rn is lower than Rn- and Rn+. In the
rightwardly ascending section in FIG. 16, since Rn is still higher
than Rn-, the control sequence advances to step S75 and then from
step S75 to step S77 so that similar processing is repeated. When
the sampling point successively advances in the leftward direction
(toward an optimum point) until Sn reaches an optimum point, Rn is
lower than Rn+ and lower than Rn-. In this instance, the control
sequence advances from step S74 to step S78, in which the value of
the offset signal Sn then is determined as an optimum value. Then,
the control circuit 42 thereafter controls the offset generation
circuit 43 to generate the optimum value continuously.
Further, similarly as in the processing illustrated in FIG. 7, a
sudden descending variation point Sm.sub.2 and a sudden ascending
variation point Sm.sub.1 are calculated. Thus, a middle point
between them can be determined as an optimum point with which the
jitters exhibit a minimum value.
In particular, in this instance, in the section of the sample
points S.sub.0 to Sn, sample values R.sub.0 to Rn are calculated in
advance as seen in FIG. 18. Then, the variation points Sm.sub.1 and
Sm.sub.2 are determined from those sample values, and a middle
point between them is determined.
FIG. 19 illustrates an example of processing in this instance.
Referring to FIG. 19, in the processing illustrated, 0 is initially
placed into the variable n first in step S91, and then in step S92,
the following equation is calculated.
where SMIN is a minimum value of the offset adjustment value, and
.alpha. is a width or step size with which the offset value is
varied stepwise.
In the present case, since n=0, S[0] is set to SMIN.
The control circuit 42 controls the offset generation circuit 43 to
generate the signal S[n] (in this instance, S[0]=SMIN). Then, the
amplitude of jitters then is detected by the level detection
circuit 41, and the value thereof is placed into R[n] (=R[0]).
Thereafter, the control sequence advances to step S93, in which the
variable n is incremented by 1 (to n=1). In step S94, it is
discriminated whether or not the variable after incremented is
lower than NUM. The character NUM represents a value given, where a
maximum value of the offset value is represented by SMAX, by
(SMAX-SMIN)/.alpha.. In other words, NUM represents the number of
samples within the focus offset scanning range.
When n is lower than NUM, since this signifies that all sampling
points are not yet sampled, the control sequence returns to step
S92, in which the following equation is calculated:
In particular, in the present processing, a value higher by .alpha.
than SMIN is set as an offset signal S[1]. Then, the amplitude of
jitters when the offset signal S[1] is generated is measured, and a
value of it is set as R[1].
Thereafter, the control sequence advances to step S93, in which the
variable n is incremented by 1, in this instance, to n=2. Then,
when it is discriminated in step S94 that the variable n (=2) is
lower than NUM, the control sequence returns to step S92 so that
similar processing is executed repetitively. In this manner,
amplitude values R.sub.0 to Rn of jitters at the sampling points of
S.sub.0 to Sn shown in FIG. 18 are obtained.
When sampling within the search range is completed in such a manner
as described above, the variable n becomes equal to NUM. Thus, the
control sequence now advances from step S94 to step S95, in which
the variable n is initially set to 1. Then in step S96, it is
discriminated whether or not the difference between the amplitude
value R[n] of the reference point at present and the preceding
amplitude value R[n-1] is lower than a reference value Th set in
advance. In particular, it is discriminated whether or not the
value of R[0]-R[1] is lower than Th. Since the rightwardly
descending characteristic is presented in a first section of the
sampling range, R[0] is sufficiently higher than R[1] (the
difference (R[0]-R[1]) between them is higher than Th). Thus, the
control sequence advances to step S97, in which a middle value
between the sampling points S[n] and S[n-1] is set as the variation
point Sm.sub.2. In other words, the following equation is
calculated:
In the present case, a middle point between S[1] and S[0] is set as
Sm.sub.2.
Then, the control sequence advances to step S98, in which the
variable n is incremented by 1 (to n=2), and then to step S99, in
which it is discriminated whether or not the variable n is lower
than NUM. When the variable n is lower than NUM, the control
sequence returns to step S96, in which it is discriminated whether
or not the value of R[1]-R[2] is lower than Th. As seen in FIG. 18,
within a period within which the jitters vary by a comparatively
great amount, the difference between the two sample values is
higher than the reference value Th. Therefore, the control sequence
advances again to step S97, in which the value of (S[2]+S[1])/2 is
placed into Sm.sub.2. In other words, the value on the side spaced
rightwardly by .alpha. from the location in the preceding cycle is
placed into Sm.sub.2.
Then in step S98, the variable n is incremented by 1 again to n=3,
and then the control sequence returns from step S99 to step S96 to
repetitively execute similar processing.
Then, as the sampling point is successively shifted rightwardly in
FIG. 18, the rate of change of jitters decreases gradually.
Thereafter, when it is discriminated that the value of R[n-1]-R[n]
is lower than Th, the control sequence advances from step S96 to
step S100. In other words, in this instance, a variation point
(sudden descending variation point) from a section in which the
rate of change of the amplitude of jitters is high to another
section in which the rate of change is low is set as Sm.sub.2.
In steps S100 et seq., a point of variation at which the rate of
change of the amplitude of jitters increases suddenly from a period
within which the rate of change gradually increases to another
period within which the rate of change increases suddenly is
detected as a sudden ascending variation point Sm.sub.1.
To this end, in step S100, it is discriminated whether or not the
value of R[n]-R[n-1] is higher than the reference value Th. Within
a period within which the sample value R[n-1] on the left side is
higher than the sample value R[n] on the right side (within a
rightwardly descending period) and within a period within which the
sample value R[n] on the right side is higher than the sample value
R[n-1] on the left side but the difference between them is small,
the value of R[n]-R[n-1] is lower than the reference value Th.
Thus, the control sequence advances from step S100 to step S101, in
which a value between S[n] and S[n-1] is placed into Sm.sub.1. In
other words, the following equation is calculated:
Then, n is incremented by 1 in step S102, and it is discriminated
in step S103 whether or not the variable n is lower than NUM-1
(whether or not the search range reaches the right end in FIG. 18).
When the variable n is lower than NUM-1, the control sequence
returns to step S100, in which similar processing is repeated for
two sample values spaced by one sample distance on the right side
in FIG. 18. Then, when the difference between the two sample values
is lower than the reference value Th, the control sequence advances
again to step S101, in which a middle value between the two
sampling points is placed into Sm.sub.1.
When the sampling point is successively shifted in the rightward
direction in FIG. 18 in this manner until the sample value R[n] on
the right side in FIG. 18 exhibits a sudden increase from the
sample value R[n-1] on the left side, the difference between them
(R[n]-R[n-1]) is equal to or higher than the reference value Th. In
this instance, a middle value between the sampling points S[n-1]
and S[n] is placed in Sm.sub.1. Then, the value then is determined
as a sudden ascending variation point Sm.sub.1.
Since the sudden descending variation point Sm.sub.2 has been
calculated in step S97 and the sudden ascending variation point
Sm.sub.1 has been calculated in step S101 in this manner, the
control sequence now advances to step S104, in which a middle point
between the variation points Sm.sub.1 and Sm.sub.2 is determined as
an optimum point. In other words, the value of (Sm.sub.1
+Sm.sub.2)/2 is set as an optimum point.
It is to be noted that, when it is discriminated in step S99 that
the variable n is equal to or higher than NUM, the control sequence
advances from step S99 to step S100. On the other hand, when it is
discriminated in step S103 that the variable n is equal to or
higher than NUM-1, the control sequence advances from step S103 to
step S104.
Where an optimum point is detected by the method illustrated in
FIG. 7 or 18, even if noise is superposed with the tracking error
signal, the RF signal or the jitters, an influence by the noise can
be reduced.
Also where an optimum focus offset position is searched for using
jitters, the processing illustrated in FIG. 3 or 9 or the
processing illustrated in FIG. 11 may be employed. Where an optimum
focus offset position is searched for by the processing illustrated
in FIG. 3 or 9, the reproduction apparatus is constructed in such a
manner as shown in FIG. 14. In particular, in this instance, the
optimum focus offset position storage circuit 33 is required. In
contrast, where the processing illustrated in FIG. 11 is employed,
the optimum focus offset position storage circuit 33 is unnecessary
as seen in FIG. 20.
While, in the foregoing embodiments, a recording and/or
reproduction apparatus of the present invention is applied to an
optical disk reproduction apparatus by way of an example, the
present invention can be applied also to recording of information
onto an optical disk.
Having now fully described the invention, it will be apparent to
one of ordinary skill in the art that many changes and
modifications can be made thereto without departing from the spirit
and scope of the invention as set forth herein.
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